As a new foiler I have no concept of speed(seems like I'm hitting 50 kts at times lol) On my ss hoverglide riding in 13 knt winds how fast do you think I'm going? Seems like I can be foiling at silly low speeds.I'm trying to keep control and once up on foil I'll sheet out and just cruise along,at this point I just want to gain feeling for foiling.

I am pretty sure you go around 10-12 knots most of the time with your bigger wing, and when REALLY fast, around 15-16 knots.

And I am not joking

Assume your question was for real ?
Most nowadays have a gps of some kind, but you can use your phone in a sealed bag under the wetsuit to track and tell you the speed, so try that and you will know

the easy way to tell is how bad it hurts when you fall.
If it feels like wakeboarding or waterskiing too fast, even when you aren't smacking down from max height, probably 20+.
If it doesn't hurt, you aren't going fast.
With my zeeko aluminum foil, I also know it's slow or bad trim if the mast is humming (probably 8-12kts), good if all is quiet (10-15ish), and "it's gonna hurt" fast when the stab starts singing (18?).
And maxed when I can't get foil height down, the foil is singing, and it feels like a windsurfing catapult fall when I go down. supposedly these foils max out around 25-30. Knowing my gear, conditions, and novice status I put myself at the low end of that. I'll worry about GPS when I get the jibes wired...
I will add though, that I have noticed people rarely try to cross my bow when foiling.
Much faster on average than kiting or most other sailboats.
Still hard to pass a fast planing dinghy under spinnaker downwind in 12-15 knots though, maybe need to loop kite to go deeper.
I think the range 12-18 knots is where most of the fun is, so far.

To figure out speed the old fashioned way, identify some landmarks/buoys 300m or more apart and count seconds between them on opposite courses. Do several runs each direction and average the time. Then use a chart/map (or google) to get the distance. This works quite well within 3-5%, comparable to a phone or cheap gps (and can be verified against gps if you doubt it).

I'm doing 15-16 knots cruising, not pushing it. If I push it I'm doing 18-19 knots. I have a Suunto Ambit. These are repeated and multiple session numbers.
When I'm doing 18-19 and fall off, it hurts. I got small concussion a few weeks back. Bam, side of head hit water. Use a gath helmet.
When I ride my bicycle to work I get up to 19knots ( 36km/hr) if I have a tail wind or a little downhill. It seems really fast.
Still, doing 25 knots and falling sounds dangerous. 50 is out of the question.

yes also at least a bit a speed freak, even if I was not able to exceed the 49 km/h on my racefoil, which is a bit of a shame , but think I am just to light, maybe will buy a smaller speed wing in the future.

So I found your topic also very interesting. Speed is the need for bigair for me. But on the other hand I now decided to slow down first and learn much about control within arials with a foil.

And yes also have done my first meters with an old moses right from the start, great foil for its time.

Personaly i like the "race" style in the very lightwinds, everything under 8-10knots, where hardly you can have any fun on the "wavestyle" and the sea is flat which is perfect for speed, would be using a big foil kite here and a race hidrofoil. Over 10-12 knots i would pick a 8-9m LEI and just carve around doing 360s, 180s, toeside tacks and playing around, with a "fast" wave hidrofoil, ive tried a slow big one, and i didnt like it, too slow no fun.